Design of partial emission type liquid nitrogen pump

High Temperature Superconductor power cable systems are being developed actively to solve the problem of increasing power demand. With increases in the unit length of the High Temperature Superconductor power cable, it is necessary to develop highly efficient and reliable cryogenic pumps to transport the coolant over long distances. Generally, to obtain a high degree of efficiency, the cryogenic pump requires a high pressure rise with a low flow rate, and a partial emission type pump is appropriate considering its low specific speed, which is different from the conventional centrifugal type, full emission type. This paper describes the design of a partial emission pump to circulate subcooled liquid nitrogen. It consists of an impeller, a circular case and a diffuser. The conventional pump and the partial emission pump have different features in the impeller and the discharge flow passage. The partial emission pump uses an impeller with straight radial blades. The emission of working fluid does not occur continuously from all of the impeller channels, and the diffuser allows the flow only from a part of the impeller channels. As the area of the diffuser increases gradually, it converts the dynamic pressure into static pressure while minimizing the loss of total pressure. We used the known numerical method for the optimum design process and made a CFD analysis to verify the theoretical performance.